Summary of the skin substitute revolution - skin coverings in the modern era of healthcare.

Skin substitutes and covers are crucial across surgical disciplines, promoting interdisciplinary collaboration to meet varied clinical needs. While some medical professionals may encounter these products infrequently in their practice, understanding their properties and applications is paramount to provide optimal patient care. In this overview, we aim to provide healthcare professionals with essential information regarding skin substitutes and covers, equipping them with knowledge to navigate their use effectively across different clinical scenarios and to optimize patient outcomes. The speed of progress in tissue engineering and regenerative medicine is notable, driven by collaborative efforts among scientists, engineers, and clinicians. Technological advancements, increased funding, and a deeper understanding of cellular and molecular processes have accelerated research and development. However, challenges remain, such as achieving vascularization in engineered tissues, addressing immune responses, and ensuring long-term functionality of regenerated organs. Despite these hurdles, the field continues to evolve rapidly, offering hope for transformative medical solutions that may redefine the treatment landscape soon. In this article, we review the current selected commercially available epidermal, dermal, and total skin substitutes for wound healing.

Advantages of simultaneous radial nerve and tendon reconstruction - a case report.

Transection of the radial nerve is frequently associated with humeral shaft fractures that are part of a very complex upper extremity injury. In the presented case, a 19-year-old man with a 10-cm radial nerve defect with a need for nerve grafting to recover complete sensory and motor deficit of the radial nerve. In our case, at the same time we provided the tendon transfer of musculus (m.) pronator teres to m. extensor carpi radialis brevis, m. flexor carpi ulnaris to m. extensor digitorum communis, m. palmaris longus to m. extensor pollicis longus, and long sural nerve graft because of an extensive zone of the injury. The assumption was that if these two procedures are performed in one surgery, it will accelerate overall recovery, restore the functionality of the upper limb more quickly, and thus enable a faster recovery.

Markers associated with genomic instability, immunogenicity and immune therapy responsiveness in Metaplastic carcinoma of the breast: Expression of γH2AX, pRPA2, P53, PD-L1 and tumor infiltrating lymphocytes in 76 cases.

BACKGROUND: Metaplastic breast cancer (MpBC) is an aggressive subtype of breast carcinoma that is often resistant to conventional chemotherapy. Therefore, novel treatment strategies are urgently needed. Immune check point inhibitors have shown activity in programmed death-ligand 1 (PD-L1) - positive metastatic triple negative breast carcinoma (TNBC), which raises the possibility that immunotherapy may also be effective in MpBC as most of the MpBCs are triple negative. The aim of the present study was to assess genomic instability and immunogenicity in tumor specimens of patients with MpBC. METHODS: A total of 76 patients diagnosed with MpBC over a 15-year period were included in the study. We performed immunohistochemical analyses for tumor cell PD-L1, immune cell PD-L1 and p53 on tissue microarrays (TMAs), analyzed stromal and intratumoral tumor infiltrating lymphocytes (TILs) from hematoxylin and eosin-stained (H&E) slides and scored gamma-H2AX (γH2AX) and phosphorylated-RPA2 (pRPA2) from whole tissue sections. We correlated marker expression with clinicopathologic features and clinical outcome. RESULTS: All tumors expressed γH2AX and pRPA2 with median expressions of 43% and 44%. P53- (68%), tumor cell PD-L1- (59%) and immune cell PD-L1-positivity (62%) were common in MpBCs. Median stromal TIL and intratumoral TIL counts were 5% and 0. The spindle and squamous cell carcinomas expressed the highest levels of PD-L1 and TILs, and carcinoma with mesenchymal differentiation the lowest. CONCLUSIONS: MpBC appears to be an immunogenic cancer with high genomic instability and frequent PD-L1-positivity, implying that check point inhibitors might be effective in MpBC. Expression levels of PD-L1 and TILs varied across different histologic subtypes, suggesting that immunotherapy might be less effective in carcinoma with mesenchymal differentiation.

Overabundant FANCD2, alone and combined with NQO1, is a sensitive marker of adverse prognosis in breast cancer.

BACKGROUND: Defective DNA repair is central to the progression and treatment of breast cancer. Immunohistochemically detected DNA repair markers may be good candidates for novel prognostic and predictive factors that could guide the selection of individualized treatment strategies. PATIENTS AND METHODS: We have analyzed nuclear immunohistochemical staining of BRCA1, FANCD2, RAD51, XPF, and PAR in relation to clinicopathological and survival data among 1240 paraffin-embedded breast tumors, and additional gene expression microarray data from 76 tumors. The antioxidant enzyme NQO1 was analyzed as a potential modifier of prognostic DNA repair markers. RESULTS: RAD51 [hazard ratio (HR) 0.81, 95% confidence interval (CI) 0.70-0.94, P = 0.0050] and FANCD2 expression (HR 1.50, 95% CI 1.28-1.76, P = 1.50 × 10(-7)) were associated with breast cancer survival. High FANCD2 expression correlated with markers of adverse prognosis but remained independently prognostic in multivariate analysis (HR 1.27, 95% CI 1.08-1.49, P = 0.0043). The FANCD2-associated survival effect was most pronounced in hormone receptor positive, HER2-negative tumors, and in tumors with above-median NQO1 expression. In the NQO1-high subset, patients belonging to the highest quartile of FANCD2 immunohistochemical scores had a threefold increased risk of metastasis or death (HR 3.10, 95% CI 1.96-4.92). Global gene expression analysis indicated that FANCD protein overabundance is associated with the upregulation of proliferation-related genes and a downregulated nucleotide excision repair pathway. CONCLUSION: FANCD2 immunohistochemistry is a sensitive, independent prognostic factor in breast cancer, particularly when standard markers indicate relatively favorable prognosis. Taken together, our results suggest that the prognostic effect is linked to proliferation, DNA damage, and oxidative stress; simultaneous detection of FANCD2 and NQO1 provides additional prognostic value.

The retinoblastoma protein pathway and the restriction point.

The emerging role of the retinoblastoma protein (pRb) as a major controller of the restriction point has been supported by recent discoveries, including pRb's ability to repress gene transcription by all three RNA polymerases, which suggests a link between DNA replication and cell growth. Convergent genetic and biochemical data provide new insights into the molecular events that are upstream of, at, and downstream of pRb phosphorylation, which is regulated by G1-phase cyclins and cyclin-dependent kinases (Cdks) and their inhibitors (CKIs). Major advances have also been made in our understanding of a key role of the pathway involving cyclin D, Cdks, CKIs, pRb and E2F both in commitment to traversing the cell cycle and in restraining oncogenesis.

Heterochromatin marks HP1γ, HP1α and H3K9me3, and DNA damage response activation in human testis development and germ cell tumours.

Heterochromatinization has been implicated in fundamental biological and pathological processes including differentiation, senescence, ageing and tumourigenesis; however, little is known about its regulation and roles in human cells and tissues in vivo. Here, we show distinct cell-type- and cancer-stage-associated patterns of key heterochromatin marks: histone H3 trimethylated at lysine 9 (H3K9me3) and heterochromatic adaptor proteins HP1α and HP1γ, compared with the γH2AX marker of endogenously activated DNA damage response (DDR) and proliferation markers in normal human foetal (n=4) and adult (n=29) testes, pre-invasive carcinoma in situ (CIS; n=26) lesions and a series of overt germ cell tumours, including seminomas (n=26), embryonal carcinomas (n=18) and teratomas (n=11). Among striking findings were high levels of HP1γ in foetal gonocytes, CIS and seminomas; enhanced multimarker heterochromatinization without DDR activation in CIS; and enhanced HP1α in teratoma structures with epithelial and neuronal differentiation. Differential expression of the three heterochromatin markers suggests their partly non-overlapping roles, and separation of heterochromatinization from DDR activation highlights distinct responses of germ cells vs. somatic tissues in early tumourigenesis. Conceptually interesting findings were that subsets of human cells in vivo proliferate despite enhanced heterochromatinization, and that cells can strongly express even multiple heterochromatin features in the absence of functional retinoblastoma protein and without DDR activation. Overall, these results provide novel insights into cell-related and tumour-related diversity of heterochromatin in human tissues in vivo, relevant for andrology and intrinsic anti-tumour defence roles attributed to activated DDR and cellular senescence.

DNA tumor virus oncoproteins and retinoblastoma gene mutations share the ability to relieve the cell's requirement for cyclin D1 function in G1.

The retinoblastoma gene product (pRB) participates in the regulation of the cell division cycle through complex formation with numerous cellular regulatory proteins including the potentially oncogenic cyclin D1. Extending the current view of the emerging functional interplay between pRB and D-type cyclins, we now report that cyclin D1 expression is positively regulated by pRB. Cyclin D1 mRNA and protein is specifically downregulated in cells expressing SV40 large T antigen, adenovirus E1A, and papillomavirus E7/E6 oncogene products and this effect requires intact RB-binding, CR2 domain of E1A. Exceptionally low expression of cyclin D1 is also seen in genetically RB-deficient cell lines, in which ectopically expressed wild-type pRB results in specific induction of this G1 cyclin. At the functional level, antibody-mediated cyclin D1 knockout experiments demonstrate that the cyclin D1 protein, normally required for G1 progression, is dispensable for passage through the cell cycle in cell lines whose pRB is inactivated through complex formation with T antigen, E1A, or E7 oncoproteins as well as in cells which have suffered loss-of-function mutations of the RB gene. The requirement for cyclin D1 function is not regained upon experimental elevation of cyclin D1 expression in cells with mutant RB, while reintroduction of wild-type RB into RB-deficient cells leads to restoration of the cyclin D1 checkpoint. These results strongly suggest that pRB serves as a major target of cyclin D1 whose cell cycle regulatory function becomes dispensable in cells lacking functional RB. Based on available data including this study, we propose a model for an autoregulatory feedback loop mechanism that regulates both the expression of the cyclin D1 gene and the activity of pRB, thereby contributing to a G1 phase checkpoint control in cycling mammalian cells.

A requirement for cyclin D3-cyclin-dependent kinase (cdk)-4 assembly in the cyclic adenosine monophosphate-dependent proliferation of thyrocytes.

In different systems, cyclic adenosine monophosphate (cAMP) either blocks or promotes cell cycle progression in mid to late G1 phase. Dog thyroid epithelial cells in primary culture constitute a model of positive control of DNA synthesis initiation and G0-S prereplicative phase progression by cAMP as a second messenger for thyrotropin (TSH). The cAMP-dependent mitogenic pathway is unique as it is independent of mitogen-activated protein kinase activation and differs from growth factor-dependent pathways at the level of the expression of several protooncogenes/transcription factors. This study examined the involvement of D-type G1 cyclins and their associated cyclin-dependent kinase (cdk4) in the cAMP-dependent G1 phase progression of dog thyroid cells. Unlike epidermal growth factor (EGF)+serum and other cAMP-independent mitogens, TSH did not induce the accumulation of cyclins D1 and D2 and partially inhibited the basal expression of the most abundant cyclin D3. However, TSH stimulation enhanced the nuclear detection of cyclin D3. This effect correlated with G1 and S phase progression. It was found to reflect both the unmasking of an epitope of cyclin D3 close to its domain of interaction with cdk4, and the nuclear translocation of cyclin D3. TSH and EGF+serum also induced a previously undescribed nuclear translocation of cdk4, the assembly of precipitable cyclin D3-cdk4 complexes, and the Rb kinase activity of these complexes. Previously, cdk4 activity was found to be required in the cAMP-dependent mitogenic pathway of dog thyrocytes, as in growth factor pathways. Here, microinjections of a cyclin D3 antibody showed that cyclin D3 is essential in the TSH/ cAMP-dependent mitogenesis, but not in the pathway of growth factors that induce cyclins D1 and D2. The present study (a) provides the first example in a normal cell of a stimulation of G1 phase progression occurring independently of an enhanced accumulation of cyclins D, (b) identifies the activation of cyclin D3 and cdk4 through their enhanced assembly and/or nuclear translocation, as first convergence steps of the parallel cAMP-dependent and growth factor mitogenic pathways, and (c) strongly suggests that this new mechanism is essential in the cAMP-dependent mitogenesis, which provides the first direct demonstration of the requirement for cyclin D3 in a G1 phase progression.

Convergence of mitogenic signalling cascades from diverse classes of receptors at the cyclin D-cyclin-dependent kinase-pRb-controlled G1 checkpoint.

The commitment of mammalian cells in late G1 to replicate the genome and divide in response to mitogenic growth factors operating via tyrosine kinase receptors depends on phosphorylation of the retinoblastoma protein (pRb), a process controlled by cyclin D-associated cyclin-dependent kinases (cdks) and their inhibitors. This study addressed the issue of whether also other mitogenic signalling cascades require activation of cyclin D-associated kinases or whether any mitogenic pathway can bypass the cyclin D-pRb checkpoint. We show that mitogenic signal transduction pathways from three classes of receptors, the membrane tyrosine kinase receptors activated by serum mitogens or epidermal growth factor, estrogen receptors triggered by estradiol, and the cyclic AMP-dependent signalling from G-protein-coupled thyrotropin receptors, all converge and strictly require the cyclin D-cdk activity to induce S phase in human MCF-7 cells and/or primary dog thyrocytes. Combined microinjection and biochemical approaches showed that whereas these three mitogenic cascades are sensitive to the p16 inhibitor of cdk4/6 and/or cyclin D1-neutralizing antibody and able to induce pRb kinase activity, their upstream biochemical routes are distinct as demonstrated by their differential sensitivity to lovastatin and requirements for mitogen-activated protein kinases whose sustained activation is seen only in the growth factor-dependent pathway. Taken together, these results support the candidacy of the cyclin D-cdk-pRb interplay for the convergence step of multiple signalling cascades and a mechanism contributing to the restriction point switch.

Cyclin D1 is dispensable for G1 control in retinoblastoma gene-deficient cells independently of cdk4 activity.

To elucidate the regulator-versus-target relationship in the cyclin D1/cdk4/retinoblastoma protein (pRB) pathway, we examined fibroblasts from RB-1 gene-deficient and RB-1 wild-type littermate mouse embryos (ME) and in human tumor cell lines that differed in the status of the RB-1 gene. The RB+/+ and RB-/- ME fibroblasts expressed similar protein levels of D-type cyclins, cdk4, and cdk6, showed analogous spectra and abundance of cellular proteins complexed with cdk4 and/or cyclins D1 and D2, and exhibited comparable associated kinase activities. Of the two human cell lines established from the same sarcoma biopsy, the RB-positive SKUT1B cells contained cdk4 that was mainly associated with D-type cyclins, contrary to a predominant cdk4-p16INK4 complex in the RB-deficient SKUT1A cells. Antibody-mediated neutralization of cyclin D1 arrested the RB-positive ME and SKUT1B cells in G1, whereas this cyclin appeared dispensable in the RB-deficient ME and SKUT1A cells. Lack of requirement for cyclin D1 therefore correlated with absence of functional pRB, regardless of whether active cyclin D1/cdk4 holoenzyme was present in the cells under study. Consistent with a potential role of cyclin D/cdk4 in phosphorylation of pRB, monoclonal anti-cyclin D1 antibodies supporting the associated kinase activity failed to significantly affect proliferation of RB-positive cells, whereas the antibody DCS-6, unable to coprecipitate cdk4, efficiently inhibited G1 progression and prevented pRB phosphorylation in vivo. These data provide evidence for an upstream control function of cyclin D1/cdk4, and a downstream role for pRB, in the order of events regulating transition through late G1 phase of the mammalian cell division cycle.

Tumors overexpressing RNF168 show altered DNA repair and responses to genotoxic treatments, genomic instability and resistance to proteotoxic stress.

Chromatin DNA damage response (DDR) is orchestrated by the E3 ubiquitin ligase ring finger protein 168 (RNF168), resulting in ubiquitin-dependent recruitment of DDR factors and tumor suppressors breast cancer 1 (BRCA1) and p53 binding protein 1 (53BP1). This ubiquitin signaling regulates pathway choice for repair of DNA double-strand breaks (DSB), toxic lesions whose frequency increases during tumorigenesis. Recruitment of 53BP1 curbs DNA end resection, thereby limiting homologous recombination (HR) and directing DSB repair toward error-prone non-homologous end joining (NHEJ). Under cancer-associated ubiquitin starvation conditions reflecting endogenous or treatment-evoked proteotoxic stress, the ubiquitin-dependent accrual of 53BP1 and BRCA1 at the DNA damage sites is attenuated or lost. Challenging this current paradigm, here we identified diverse human cancer cell lines that display 53BP1 recruitment to DSB sites even under proteasome inhibitor-induced proteotoxic stress, that is, under substantial depletion of free ubiquitin. We show that central to this unexpected phenotype is overabundance of RNF168 that enables more efficient exploitation of the residual-free ubiquitin. Cells with elevated RNF168 are more resistant to combined treatment by ionizing radiation and proteasome inhibition, suggesting that such aberrant RNF168-mediated signaling might reflect adaptation to chronic proteotoxic and genotoxic stresses experienced by tumor cells. Moreover, the overabundant RNF168 and the ensuing unorthodox recruitment patterns of 53BP1, RIF1 and REV7 (monitored on laser micro-irradiation-induced DNA damage) shift the DSB repair balance from HR toward NHEJ, a scenario accompanied by enhanced chromosomal instability/micronuclei formation and sensitivity under replication stress-inducing treatments with camptothecin or poly(ADP-ribose) polymerase (PARP) inhibitor. Overall, our data suggest that the deregulated RNF168/53BP1 pathway could promote tumorigenesis by selecting for a more robust, better stress-adapted cancer cell phenotype, through altered DNA repair, fueling genomic instability and tumor heterogeneity. Apart from providing insights into cancer (patho)biology, the elevated RNF168, documented here also by immunohistochemistry on human clinical tumor specimens, may impact responses to standard-of-care and some emerging targeted cancer therapies.

Abnormal patterns of D-type cyclin expression and G1 regulation in human head and neck cancer.

D-type cyclins are proto-oncogenic cell cycle regulators implicated in the pathogenesis of several types of cancer. Amplification of the cyclin D1 gene has been described in 30-50% of human head and neck squamous cell carcinoma (HNSCC). Using immunohistochemistry on archival specimens of human HNSCC and a mAb DCS-6, which is specific for cyclin D1, strong positivity was found in nuclei of 9 (17%) of 52, a moderately elevated signal in 16 (31%) of 52, and weak staining comparable with normal tissues in 27 (52%) of 52 patients. Immunoblotting analysis of five HNSCC-derived cell lines showed three distinct spectra of D-type cyclin proteins: cyclin D1 only (in UMSCC-2 and UMSCC-22b cell lines with 11q13 amplification), cyclins D1 and D3 (in HN5 and HN6), or cyclins D1, D2, and D3 (in UMSCC-1). Electroporation of neutralizing antibodies demonstrated requirement for cyclin D1 in cell cycle progression of all five HNSCC cell lines. Cyclin D2 was essential and showed a cooperative effect with cyclin D1 in positive regulation of G1 in UMSCC-1 cells. These data are consistent with the proposed oncogenic role of cyclin D1 in HNSCC and open up the way for immunohistochemical assessment of cyclin D1 aberrations in archival clinical specimens. It is also suggested that excessive levels of cyclin D1 alone or cooperative effects of several D-type cyclin proteins may lead to deregulation of G1 control in distinct subsets of human HNSCC. These results are discussed in the context of possible functional redundancy of D-type cyclins and the role of the D-type cyclin/p16-CDKN2/pRB pathway in tumorigenesis.

The p16-cyclin D/Cdk4-pRb pathway as a functional unit frequently altered in melanoma pathogenesis.

The p16Ink4/CDKN2, D-type cyclins, their partners Cdk4/Cdk6, and pRb constitute a G1 regulatory pathway commonly targeted in tumorigenesis. Genetic, immunochemical, and functional cell cycle analyses showed abnormalities of this pathway in each of 22 human melanoma cell lines examined. Normal melanocytes and all melanoma lines expressed Cdk4, Cdk6, and cyclins D1 and D3. The tumor suppressors p16Ink4/CDKN2 and pRb were lost in 17 and 4 cases, respectively, due to various genetic mechanisms, including transcriptional block of p16 and nonsense mutations of RB1. Ectopic expression of p16 prevented S-phase entry of Rb+/p16- but not Rb-deficient melanoma lines. The SK29-MEL-1 cell line harboring an R24C mutation in Cdk4 expressed wild-type pRb and overabundant p16, the latter preventing endogenous Cdk6 but not Cdk4 from associating with cyclin D1. Microinjection of cyclin D1-neutralizing antibody arrested the SK29-MEL-1 cells in G1, whereas pl6 did not, indicating that the cyclin D1/Cdk4-R24C complex is required for G1 progression, and the resistance of the complex to p16 in vivo. These data strongly support the candidacy of Cdk4 as a novel proto-oncogene, provide further evidence for the p16-cyclin D/Cdk-pRb pathway as a functional unit, and suggest that deregulation of this checkpoint may represent a common step in the multistep progression of sporadic malignant melanomas.

DNA damage-activated kinase Chk2 is independent of proliferation or differentiation yet correlates with tissue biology.

The Chk2 kinase is a tumor suppressor and key transducer of DNA-damage checkpoints. We show that the human Chk2 protein is relatively stable, nuclear, and responding to gamma-radiation throughout the cell cycle. Contrary to the retinoblastoma protein-regulated, labile Chk1 kinase restricted to S-G(2) phases, Chk2 remains activatable even in quiescent and differentiating cells. In human tissues, Chk2 is homogeneously expressed in renewing cell populations such as epidermis or intestine, heterogeneous in conditionally renewing tissues, and absent or cytoplasmic in static tissues such as muscle or brain. These data highlight striking differences between Chk2 and Chk1 and show unexpected correlation of Chk2 expression with tissue biology.

Cyclin D1 oncoprotein aberrantly accumulates in malignancies of diverse histogenesis.

Cyclin D1 is a cell cycle regulator essential for G1 phase progression and a candidate proto-oncogene whose deregulated expression has been implicated in pathogenesis of several types of cancer. We have examined expression of cyclin D1 in 212 primary tumours of five histogenetically distinct types by immunohistochemistry and found strong aberrant accumulation of the protein in 21%, and a moderate overabundance in further 25% of cases. While the abnormalities were more frequent in carcinomas of the breast, i.e. the cancer type known for cyclin D1 gene amplification, aberrant expression was also seen in significant subsets of colorectal cancers, soft tissue sarcomas, uterine carcinomas and malignant melanomas. Comparison of distinct stages of tumour progression showed concordant cyclin D1 patterns in the in situ vs invasive breast carcinoma components (n = 37) and between primary and metastatic lesions (n = 51) of several tumour types. The specificity of the immunohistochemical data was supported by immunoblotting analysis of tissue and tumour lysates, and the tumour-specific over-expression was confirmed by computer-assisted image analysis. These observations suggest that alterations of cyclin D1 expression represent a common feature of malignancies of diverse histogenesis and indicate that both the spectrum of tumour types and the frequency of cyclin D1 aberrations significantly exceed previous estimations based on genetic analyses.

Cyclin D3: requirement for G1/S transition and high abundance in quiescent tissues suggest a dual role in proliferation and differentiation.

The mammalian D-type cyclins D1, D2, and D3 activate the cyclin-dependent kinases CDK4 and CDK6 in G1 and thereby promote the cell's commitment to enter S phase. To elucidate the extent of functional overlap among the D-type cyclins, we have examined several aspects of the least characterized member of this subfamily of G cyclin proteins, cyclin D3. Microinjection of cyclin D3-neutralizing antibody inhibited G1/S transition in human (IMR-90) and rat (R12) diploid fibroblasts, indicating that analogous to cyclins D1 and D2, cyclin D3 is essential for timely progression through G1. In contrast to cyclins D1 and D2, cyclin D3 was (i) ubiquitously expressed among a panel of 70 human cultured cell types; (ii) strongly upregulated upon induction of HL-60 leukaemia cells to differentiate; and (iii) accumulated to high levels in a wide range of quiescent cell types in mouse and human differentiated tissues. Complementary analyses of human biopsies and mouse tissues at different stages of foetal and postnatal development revealed lineage-dependent transient or long-term accumulation of the cyclin D3 protein, correlating with initiation/establishment or maintenance of the mature phenotypes, respectively. Our data support the notion that the biological roles of the individual D-type cyclins are not fully redundant, and suggest a possible dual role for cyclin D3 in cell proliferation and induction and/or maintenance of terminal differentiation.

Lack of p19INK4d in human testicular germ-cell tumours contrasts with high expression during normal spermatogenesis.

p19INK4d, a member of the INK4 family of cyclin-dependent kinase inhibitors, negatively regulates the proto-oncogenic cyclin D/CDK4(6) complexes whose ability to phosphorylate the retinoblastoma tumour suppressor (RB) promotes G1/S transition. In contrast to the related p16INK4a tumour suppressor, expression patterns of 19INK4d in human tissues and tumours remain unknown. As the RB pathway is commonly targeted in cancer, and mouse models suggest a role for p19INK4d in spermatogenesis, we examined the abundance and localization of p19INK4d in the human testis, both during normal development and at various stages of germ-cell tumour pathogenesis. Our data show that the p19INK4d protein is abundant in spermatocytes of normal human adult testes, whereas virtually no p19INK4d is detectable in testicular cancer, including the preinvasive carcinoma in situ stage. Together with the lack of p19INK4d in human foetal germ cells, these results support the concept of foetal origin of the testicular germ-cell tumours, and help better understand the emerging role of the RB pathway in spermatogenesis and tumorigenesis in the human testis. Oncogene (2000) 19, 4146 - 4150

Aberrant p27Kip1 promoter methylation in malignant melanoma.

p27Kip1 is a regulator of the mammalian cell cycle and a putative tumor suppressor. Distinct altered patterns of p27Kip1 protein expression are found in a variety of human carcinomas, and p27Kip1 expression levels usually correlate directly with disease-free survival. The mechanism(s) by which p27Kip1 expression is reduced or lost during tumorigenesis remains unclear. Specific alterations of the p27Kip1 gene, including mutations and homozygous deletions, are exceedingly rare in human cancers. We have used methylation-specific PCR and bisulfite genomic sequencing to examine the methylation status of p27Kip1 in 61 primary and metastatic tumors and 35 cell lines from patients with malignant melanoma. Dense methylation of a CpG island in the promoter region of p27Kip1 was detected in four of 45 metastatic tumors (9%) and three of the cell lines (9%), including two cell lines established from two different metastases from the same patient. Examination of a naturally occurring, allele-specific sequence variant demonstrated that p27Kip1 methylation is associated with transcriptional silencing in situ. Cell lines with p27Kip1 methylation showed retention of the wild-type allele and detectable p27Kip1 protein whose abundance was reduced compared with normal melanocytes. Collectively, our data suggest that DNA methylation may be a cause of monoallelic p27Kip1 silencing in malignant melanoma, which would support a role for p27Kip1 haploinsufficiency in human cancer.

Cyclin D2 is a moderately oscillating nucleoprotein required for G1 phase progression in specific cell types.

To explore regulation and function of cyclin D2, a candidate cell cycle-regulatory proto-oncogene, we examined subcellular localisation, cell type- and cell cycle-dependent expression, and requirement of cyclin D2 protein for G1 progression, in a panel of 40 human normal and cancer cell types. Except for lymphoid cells and sarcoma cell lines, expression of cyclin D2 was considerably more restricted than that of cyclin D1, whereas both D-type cyclin proteins were low or undetectable in cells lacking functional retinoblastoma gene product. In G1 cells, the cyclin D2 protein was more resistant to extraction and localised predominantly to nuclei, whereas it became more soluble and distributed in both nuclei and cytoplasm from G1/S transition onwards. Centrifugal elutriation and multiparameter flow cytometry analyses of several cell types showed moderate cell cycle oscillation with maximum levels of the cyclin D2 protein reached in late G1. Microinjection and/or electroporation of antibodies to cyclin D2 during G1 arrested the cyclin D2-expressing lymphocytes, breast myoepithelium, and U-2-OS sarcoma cells in G1 phase, whereas cyclin D2-negative cell types were unaffected by such treatment. Consistent with the putative proto-oncogenic role of cyclin D2 in specific cell types, our data show that this G1 cyclin has properties closely resembling those of cyclin D1, including the essential positive role in regulation of G1.